The present invention relates generally to a method of geophysical exploration and, more particularly, to an improved method of gravimetric exploration employing satellite derived gravity data and surface acquired gravity data.
Most gravimetric surveys carried out in the search for oil and gas as well as for mineral and tectonic studies are designed for reconnaissance of large, previously unexplored areas. Where little or no geological information is available for a region, the first question to be answered by a gravimetric survey is whether or not sufficient sedimentary materials exist to conduct more detailed and costly investigations. Since variations in gravity depend upon changes in the density of earth formations in the vicinity of a measuring site, gravimetric surveys can be employed to determine the extent of sedimentary materials. Additionally, gravimetric surveys can be employed to locate faults, anticlinal structures and salt domes.
More recently, a variety of techniques have been developed for deriving gravity data from satellite altimeter data as described by R. C. A. Zandbergen in "Satellite Altimeter Data Processing: From Theory To Practice," Delft University, 1990. Consequently, worldwide satellite derived gravity data sets are now available at extremely attractive prices. However, such satellite derived gravity data are comprised principally of low frequency information which is too sparse (i.e., typical satellite tracks can be separated one from another by several kilometers) to provide sufficient detail to an explorationist in locating and mapping either sedimentary basins or structural faulting. While satellite derived gravity data sets hold out the possibility of extremely low cost and broad marine coverage, they have largely been of little value to explorationists who depend upon the greater resolution and more selective siting of surface acquired gravity data sets.
The present invention provides explorationists with a novel method of gravimetric exploration which overcomes the historical obstacles to utilizing satellite derived gravity data and thus taking advantage of both its low cost and broad coverage. Moreover, the present invention provides a novel method for referencing separate, non-overlapping surface acquired gravity data sets to a common reference or datum so as to extrapolate interpretive results and conclusions from one area to another.